In response to the increased need for higher bit rate and more efficient transmission of packet data over cellular networks, the Wideband Code Division Multiple Access (WCDMA) Third generation Partnership project (3GPP) Release 5 extended the WCDMA specification with the High Speed Downlink Packet Access (HSDPA), and Release 6 introduced Enhanced Dedicated Channel (E-DCH), often referred as Enhanced Uplink (EUL) or High Speed Uplink Packet Access (HSUPA). HSDPA and HSUPA together are called High Speed Packet Access (HSPA) which greatly improves the achievable bit rate over the air interface. 3GPP Release 7 introduced higher-order modulation and multiple input multiple output (MIMO) for HSDPA to further improve the achievable bit rate.
Similarly, a primary objective of a multi-carrier (MC) system is to achieve high data rate. A multi-carrier arrangement with frequency division duplex (FDD) can be described as a set of downlink carriers linked to a set of uplink carriers. The downlink carriers can be adjacent or non-adjacent in the frequency domain, and the same holds for the uplink carriers. Multi-carrier arrangements can also be used in time division duplex (TDD) systems. The component carriers in a multi-carrier system may also belong to different frequency bands. As one example, WCDMA/HSPA operating on multiple 5 MHz carrier frequencies is referred to as Multi-Carrier WCDMA or Multi-Carrier HSPA. In an Evolved Universal Mobile Telecommunications System Terrestrial Radio Access Network (E-UTRAN) system, multiple component carriers such as four 20 MHz carriers in the downlink and two 20 MHz in the uplink (for FDD) can be used to enhance the data rate. So a multi-carrier system uses more than one carrier in the downlink and/or the uplink. One of the multi-carriers is called the primary or anchor carrier and the remaining one(s) is (are) called secondary or supplementary carriers.
The anchor carrier contains all physical channels including all common control channels. The secondary carriers may or may not contain all physical channels; for instance, they may lack some of the common downlink control channels. The anchor carrier in the downlink and in the uplink (i.e., if there is more than one carrier in uplink) should support legacy operation based on a single carrier, which means the downlink anchor carrier should contain all common channels so that the legacy single-carrier User Equipments (UEs) are served. A multi-carrier UE also needs the anchor carrier to transmit all common control channels for acquisition of the frame timing, neighbor cell measurements, etc. Any single-carrier system can be evolved to a multi-carrier system to increase data rate. The future advancements of HSPA, E-UTRAN, and other systems will likely result in multiple carriers both in the uplink and the downlink, (e.g., 4 downlink carriers and 2 uplink carriers).
Different types of receivers exist. Some can receive multi-carrier transmissions—others cannot. Some receivers have interference cancellation capability—some do not. Even for those that do have interference cancellation capability, there are differences in those capabilities. For example, one type of receiver might be able to specifically cancel inter-cell interference, while another type of receiver cannot. The inter-cell interference is contributed by the signals transmitted from the neighboring cells.
Different types of inter-cell interference cancelling receivers exist. Some will attempt to explicitly estimate the characteristics of the radio propagation channel through which the interference is passing in order to characterize the interference as it is seen on the receiver end. Others attempt to directly characterize the interference as it is seen on the receiver end without any explicit estimation of the radio propagation channel.
For receivers that attempt to characterize the radio propagation channel through which the interference is passing, the channel responses of all (or at least the strongest) neighboring cells on all frequencies need to be estimated on a regular basis, e.g., once every slot/sub-frame (660 μs for a WCDMA system). This channel response processing requires significant computational resources.